Peel and wash the carrots and potatoes and cut them into pieces. Peel and chop the onion. Fry everything in hot oil and add 3⁄4 l water and broth. Bring to the boil and simmer for about 15 minutes.
Dice the toast. Fry bacon in hot butter until crisp, take out. Roast toast in hot fat. Stir the crème fraiche into the soup, puree. Season with salt, pepper and sugar. Serve with bacon and croutons.